1. Field of the Invention
The present invention relates in general to methods of disposing of halogenated hydrocarbons. More specifically, the present invention relates to the formation of a commercially viable glass that incorporates halogenated refrigerants such into the glass.
2. Description of the Prior Art
The need for devices to effectively treat and dispose of waste materials without creating undue environmental contamination has been recognized for many years. Incinerators and vitrification devices have been used to reduce municipal solid wastes to ash which must then be disposed of by conventional means, such as burial in a landfill. Incinerators have also been either used for, or proposed for, the disposal of other forms of commonly occurring waste products; in particularly, halogenated organic compounds. The resultant product from the incineration is typically a halide free ash. Vitrification is used to encapsulate the incinerator ash. When halogens are contained within such waste material, the halogens create unique problems, which are not adequately addressed by conventional treatment methods. In particular, a method of treating refrigerant hydrocarbons such as chlorofluorocarbons (CFCs) or hydrogenated chlorofluorocarbons (HCFCs) is needed.
There have been several methods of disposing of hydrogenated compounds and CFC refrigerants. Webster in U.S. Pat. No. 5,416,247 discloses a method of disposing of halogenated hydrocarbons whereby the compounds are reacted with an oxide or carbonate of an alkaline earth metal at elevated temperature, thus creating a halide salt that can be placed in a landfill. Scholz et al. in U.S. Pat. No. 5,709,734 reacts the CFC or other halogenated compound with a solid sorbent material such as iron oxyhydroxide at elevated temperatures, the halogen thereby reacting with the solid sorbent and being disposed of. Zachariah et al. in U.S. Pat. No. 5,936,137 discloses a method whereby the vapor of an alkali metal is reacted with the halocarbon gas directly, thus leading to millisecond time-scale reactions. The vapor metal halide product is condensed and then disposed of.
The incineration of wastes has also been used to encapsulate wastes into a glass which immobilizes the wastes for safe landfill disposal. The devices described by Chapman in U.S. Pat. Nos. 5,443,618 and 5,354,355 are such devices, wherein feed material is converted to a glassified material. A method of disposing of halogenated compounds by forming a glass is described by Shaw et al. in U.S. Pat. No. 5,678,244, wherein a molten bath is created having a molten phase and a vitreous phase, the vitreous phase having calcium, silicon and aluminum oxides. The halogenated compound is directed to the molten phase wherein the halogen dissociates from the compound and reacts with the vitreous phase. The Shaw et al method then takes the inorganic halogen compound which is formed and draws it away from the molten material and disposed of.
Plasma vitrification of waste materials is described by McLaughlin et al. in U.S. Pat. No. 5,637,127, wherein hazardous wastes are directed into a plasma of between 2000xc2x0 C. and 10,000xc2x0 C. in the presence of glass-forming materials such as silicon dioxide and boron oxide to form a glass. Forsberg et al. in U.S. Pat. No. 5,613,241 describes yet another method of waste disposal using incineration and/or vitrification. This process provides a bath of molten glass containing a sacrificial metal oxide such as lead oxide or bismuth oxide capable of reacting with the halogen in the waste material. Once reacted, a metal salt is formed which becomes a gas at the temperatures of the molten glass. This gas is then drawn off, reacted with aqueous metal hydroxides, and ultimately converted to a harmless salt. In this process, the halogen, such as chlorine or fluorine, is not incorporated into the final glass material. The glass material is then disposed of. In this process, a glass is made of such materials such as lead borate, bismuth borate, borosilicate glasses, silica glasses, glass ceramics, and polymeric aluminum phosphate glasses.
There are several problems with prior art methods of treating halogenated compounds by incineration and/or vitrification. One major drawback is the use of such compounds as lead oxide in reacting the halide. Lead itself is a harmful environmental contaminate and thus, it is advantageous to avoid its use. Further, the prior art processes leave behind chlorine and fluorine salts. Although these may be harmless, they to must also be disposed of. Since these salts are water soluble, they cannot be simply placed into landfills, etc. Also, the prior art processes leave behind material that must be disposed of, with no commercial value.
Therefore, there is a need for an improved method of disposing of halogenated compounds; and in particular, gaseous and liquid compounds such as CFCs and HCFCs refrigerant.
It is thus an object of the present invention to provide an improved method of destroying and disposing of environmentally hazardous CFCs and HCFCs.
It is yet another object of the present invention to provide a method of vitrification of waste containing halogenated compounds, the glass resulting from the process being commercially viable and thus avoiding landfilling.
These and other objects are achieved by providing a two stage process of incineration of CFCs and HCFCs followed by vitrification of the waste into a commercially viable glass. In the first stage, the hydrogenated compounds are reacted at elevated temperature with water and a metal oxide such as calcium oxide to form a halide salt and carbon dioxide. In the second stage of the process, the brine slurry is reacted at elevated temperature with the carbon dioxide from stage one and glass-forming raw materials such as silicon dioxide to produce a glass. The final glass product incorporates the halide into the glass.
Additional objects, features and advantages will be apparent in the written description which follows.